1. Field of the Invention
The invention relates to a display system and, more particularly, to a system which can deal with various display modes.
2, Related Background Art
In recent years, in a computer system, as a display graphic card for displaying an image from a computer to a monitor, graphic cards having various display modes (for example, resolutions in the horizontal and vertical directions, the number of display colors) have been proposed. It is also required that a display for receiving video signals from those graphic cards through a display controller and displaying them can deal with various display modes.
However, a conventional system among the graphic card, display controller, and display has the following problems.
(1) A resolution and the number of display colors of the display cannot be rapidly switched in accordance with changes in resolutions and numbers of display colors in the horizontal and vertical directions of video data which is sent from the graphic card.
For example, a CRT display called a multiscan recognizes changes in resolutions in the horizontal and vertical directions of the input video data by respectively detecting periods and polarities of horizontal and vertical sync signals in the video data, thereby changing a resolution on the display side on the basis of information of the recognition result. According to such a method, it takes a certain amount of time to confirm the periods of the horizontal and vertical sync signals and the display mode cannot be rapidly switched.
(2) The number of colors of the video data sent from the graphic card side cannot be recognized. An accurate resolution cannot be recognized as well (this is because a dot clock synchronized with a sampling frequency of the video data is not obtained).
(3) When it is necessary to change driving conditions of the display in a real-time manner from the graphic card side, such information cannot be transmitted and processed between the conventional graphic card and the display.
For example, in the display of a matrix construction, such necessity is useful in case of performing a control in a manner such that when a driving period has to be raised in accordance with the number of scanning lines of the video data which is supplied from the graphic card side, information such as the number of scanning lines is received from the graphic card side and, in order to raise the driving period in accordance with such information, a driving voltage or the like is raised.
(4) When the number of valid bits in a data bus for transmitting the video signal, namely, the number of valid bits in the data bus of a plurality of bits connected in parallel and a bit construction (bits/pixel) per pixel differ for every graphic card, the information of the data bus and a data transmission format cannot be recognized on the display side, so that the operations cannot be performed on the display side such that only the valid data is extracted and only the video data is sorted without a gap and an image corresponding to each video data is displayed.
(5) There is no means for informing the graphic card side of the driving conditions and information from the display controller when a power source is turned on.
(6) When the graphic card side and the display and display controller side operate from different power sources, there is no means for judging a state regarding whether or not the information can be transmitted between the graphic card and the display controller.